This invention relates generally to blade containment systems for turbomachinery and more particularly to a blade containment system for gas turbine engines having a textured surface that dulls sharp corners and edges of impacting fan blades.
Numerous applications exist for turbomachinery, such as gas turbine engines used to propel a variety of aircraft. One such gas turbine engine is the high bypass turbofan engine, which typically includes a large, ducted fan placed at the front of the engine. The fan serves to produce greater thrust and reduce specific fuel consumption. During the operation of such engines, there is a remote possibility that a foreign body, such as a bird, could impact the fan and cause severe fan damage. That damage could result in part or all of a fan blade becoming detached from the hub and impacting the fan casing. Such a detached fan blade could cause considerable damage to the aircraft powered by the engine if it were not contained by the fan casing. Similar damage could also result if the fan blade suffered failure through fatigue.
In order to prevent such damage, various containment systems have been employed. Fan blade containment systems have traditionally included an annular containment casing manufactured from a high strength material with an adequate radially extending shell thickness to absorb the kinetic energy of an impacting fan blade. More recent containment systems have employed various nesting areas defined by inner and outer annular casings which may include honeycomb structures therein. In addition, ballistic material such as an aromatic polyamide fiber may be wrapped around the casing structure.
Typically, a fan blade released from the hub will obliquely impact the containment structure such that an outer edge or comer of the fan blade will make initial contact with the containment structure. Under such circumstances, the impacting load is concentrated in a relatively small area, which means that the released fan blade can inflict damage to the containment structure and the engine, and could possibly pass completely through the containment casing.
One containment system that addresses this problem is disclosed in U.S. Pat. No. 5,403,148 issued Apr. 4, 1995 to James M. Forrester. This system provides a protective barrier positioned on the interior surface of the containment casing to serve as a ballistic barrier in the event that one or more blades are released. The barrier is formed by securing a number of tiles to the interior surface of the containment casing. The tiles form a substantially continuous barrier layer over the casing's interior surface. When struck by a fan blade, one or more tiles impacted by the blade serve to distribute the impact, so as to enhance the ability of the containment casing to withstand the impact. The tiles are formed from a hard material, such as a ceramic composite, which promotes the ability of the tiles to distribute a highly localized impact inflicted by a fan blade. The use of the tiles is compatible with typical structure and design configurations of turbofan engines and can accommodate acoustic liners that are typically installed in the forward section of the containment casing.
In addition to deflecting and distributing the force of the impact, the barrier of U.S. Pat. No. 5,403,148 has also been found to dull the sharp edges and corners of the fan blade upon impact, so as to further reduce the ability of the fan blade to pierce the containment casing. The dulling action of the barrier is attributed to the fact that when a blade is released, it impacts the barrier obliquely and travels perpendicularly across the junctions between adjacent tiles. Thus, these junctions, which define small discontinuities in the barrier layer, provide a source of planing action on the fan blade that removes slivers of material from the impacting blade. However, while the tile junctions do cause removal of material from an impacting blade, the degree to which the blade is dulled is limited by the number of junctions that can be feasibly provided in the barrier.
Accordingly, it would be advantageous to provide an improved containment casing for turbomachinery in which the capability of the barrier to dull an impacting blade is enhanced.